The present invention relates to a damage tolerant microstructure for lamellar alloys and to a method of producing same.
The current microstructure of lamellar γTiAl alloys is composed of an equiaxed (prior β) grain structure with planar lamella as shown in FIG. 1. The grains or lamellar colonies themselves exhibit a lamellar stack of TiAl (γ) and Ti3Al (α2) platelets such as that shown schematically in FIG. 2. Interlaminar or intralaminar shear between the layers of the lamellar stack has been identified in fatigue and fracture tests as one of the principal mechanisms leading to monotonic and cyclic crack formation, such as that shown in FIG. 3, in gamma TiAl alloys possessing a lamellar microstructure. High and low cycle fatigue fractures and near threshold small crack growth test fractures show interlaminar shear at their failure origins below 1200 degrees Fahrenheit.